(1) Field of the Invention
This invention generally relates to environmental sensing and more particularly to an apparatus for obtaining a profile of a particular environmental parameter, such as temperature, in an environment, such as the ocean.
(2) Description of the Prior Art
Many processes can be enhanced by an accurate measurement of particular environmental parameters. For example, the quality of information available from sonar hydrophone arrays can be enhanced when environmental parameters such as the temperature, salinity, and density of the water at different depths are known. These parameters directly affect the speed of sound through the water. Temperature is a dominant variable with respect to the speed of sound. Accurate knowledge in the form of a profile of temperature versus depth is particularly useful to determine the environmental effects on the acoustic waves received at a sonar hydrophone array.
The current method of obtaining such a temperature profile involves the use of an expendable bathythermograph. A bathythermograph comprises a thermistor mounted in a weighted body that is deployed over the side of a ship. Conductors connect the body to the ship and carry the thermistor measurement signal. As the bathythermograph sinks, its depth and the measured water temperature are recorded. At some point, however, the bathythermograph is released, so each bathythermograph provides only one temperature profile. In conventional sonar operations the profiles are dynamic with respect to time and position so many such profiles must be obtained. Consequently obtaining temperature profiles with expendable bathythermographs becomes a very expensive and time consuming task.
A number of patents disclose diverse hydrophone arrays. For example, U.S. Pat. No. 3,885,515 to Caldwell, Jr. et al. discloses a rigid line array suspension system that has negative buoyancy with three forward floats of double ogival shape with a buoyancy equal to or slightly greater than the negative buoyancy of the array attached to the tow cable. A linear hydrophone array is disposed along the cable, and a drogue line controls the depth of the array.
U.S. Pat. No. 4,295,212 to Swenson discloses a linear acoustic array to be towed. A flexible cable has strands that are woven or braided into a tube. It is possible to separate the strands sufficiently to insert a hydrophone and multiplexer assembly at each of a plurality of specified locations such that each hydrophone or multiplexer can be readily connected into or removed from a two wire system.
U.S. Pat. No. 5,052,222 to Stoepfel discloses a multi-unit water depth sensor system. This system includes an array with an air bubbler type depth gauge to specify the depth of an attached element in the ocean.
Other patents disclose plural thermistors and other sensors to monitor a component or individual parameter during normal use or activity. U.S. Pat. Nos. 3,633,191 and 3,748,655 to Engelhardt et al., for example, disclose electrical systems with temperature transducers spaced along an electrical conductor. The transducers and related equipment monitor the temperature of the conductor thereby to measure conductivity changes. U.S. Pat. No. 3,611,332 to Slater discloses a self-contained underwater telemetry system for transmitting biophysical data from a freeswimming diver through the water to a receiving station.
None of the foregoing references or prior art bathythermographs provide a continuous measurement of any environmental parameters such as ocean temperature. Other than the bathythermograph, none have the capability of providing a profile of the variation of temperature against some other parameter such as depth. More specifically, none of the prior art references seem capable of obtaining a continuous measurement of sea water temperature as a function of depth that is particularly adapted for use with towed cables and hydrophone arrays. Moreover, none disclose a system that can be reusable in a towed hydrophone array environment.